Bisphenols such as 2,2-bis(4'-oxyphenylpropane), or bisphenol-A, and 2,2-bis(4-hydroxyphenyl)butane, or bisphenol-B, are made by a condensation reaction of phenol with ketones, as for example with acetone for bisphenol-A, or with methyl ethyl ketone for bisphenol-B. Similar condensation reactions occur between phenol and aldehydes. Such condensation reactions are acid catalyzed, and particularly advantageous acid catalysts for the reactions are strong-acid cation exchange resins which carry the anionic portion of the acid on a solid substrate, allowing its easy removal at the completion of the reaction.
A particular problem with making bisphenol-A using cation exchange resins as the acid catalyst is that the crude bisphenol-A product may be strongly colored, and this color, unless removed, carries through into products, such as fibers, transparent sheet for glazing and the like, made from the bisphenol-A and having particularly stringent requirements for low color.
Impurities, particularly those such as sulfonic acid residues which lead to decomposition during distillation, have been removed from bisphenol-A by treating the crude bisphenol-A with anion exchange resins prior to its distillation (Faler et al., U.S. Pat. No. 4,766,254), but this treatment is a separate step from the reaction which produces the crude bisphenol-A. It would be highly advantageous to produce bisphenols such as bisphenol-A with low color directly from the condensation reaction.